SEOUL (Korea Herald/Asia News Network) - Over 83 per cent of Middle East respiratory syndrome (Mers) transmissions in South Korea were linked to five "super-spreaders" during the outbreak in South Korea this summer, the country's Centers for Disease Control and Prevention (CDC) said on Sunday (Oct 25).
The virus, considered a deadlier but less infectious cousin of Severe Acute Respiratory Syndrome (Sars), has infected 186 people in South Korea and killed 37 of them since its outbreak in May.
The latest casualty was announced earlier on Sunday. The patient, aged 66, was said to be cured of the disease but had been battling an acute lung ailment that was a complication resulting from the virus.
Following the latest death, the fatality rate of the disease in Korea rose from 19.4 per cent to 19.9 per cent.
The CDC said five patients, all of whom had pneumonia, transmitted the virus to 153 of the 184 patients diagnosed between May 20 and July 13. Patient No. 14 alone spread the virus to 85 people during his stay at Samsung Medical Center, the CDC said in its report.
The CDC termed patients who have transmitted the virus to at least four people are classified as super spreaders.
Two of the total 186 infected patients have been excluded from the denominator as their transmission routes remain uncertain, the CDC said.
This is the CDC's first such report on the Mers outbreak.
The median age of the super spreaders was 41 years and they all contacted hundreds of people while staying at their respective medical facilities. Four of them were men.
Patients 1, 14 and 16 had severe coughs and infected 28 people, 85 people, and 23 people, respectively. On the other hand, Patient 15 and patient 76, who rarely coughed, infected six people and 11 people, respectively, the report said.
These patients were hospitalised for an average of 10 days, and the number of people who came into close contact with them ranged from 288 to 805.
While patient No. 14 wore a mask intermittently, other super-spreaders did not wear one. None received aerosol-generating treatment.
Of the 186 patients infected across 16 hospitals, some 44.1 per cent of the cases were patients exposed in hospitals, 32.8 per cent were caregivers, and 13.4 per cent were health care personnel.
The most common presenting symptom was fever and chills. The estimated incubation period was 6.83 days and the serial interval was 12.5 days.
The report said the respiratory droplet route is seen as the most likely method of transmission but that further survey is currently ongoing.
The report also confirmed failed preventive measures in the early stage.
Patient No. 1 started developing fever and myalgia on May 11 after returning from a business trip to Bahrain, the United Arab Emirates and Saudi Arabia. His diagnosis did not come until May 20, partly due to a failure of him telling medical staff in his first several hospital visits the countries he had travelled to .
By then, he had already come into contact with over 600 people. Twenty-six cases of infection were confirmed among these initial contacts, and consecutive transmission via hospitals rapidly proceeded throughout the nation, the report explained.
Even upon the first diagnosis, only three were placed in isolation. The number then increased to 64 the next day and to 120 upon the diagnosis of the fifth patient. Those who were not placed in isolation soon enough further transmitted the virus at other hospitals, some of them becoming super-spreaders.
The analysis showed that the mortality rate of those aged 65 and over was almost eight times higher than that of younger patients.
A history of diabetes, malignancy and the presence of underlying respiratory disease, cardiac disease and chronic kidney disease were also significantly associated with mortality.
Mers is a viral disease that is still fairly new to humans. No vaccine or treatment is currently available for the disease, whose fatality rate is around 36 per cent globally.
Seoul had declared the outbreak effectively over at the end of July, but earlier this month a 35-year-old man believed to have been cured of the virus was rediagnosed.